In a molding method for molding a mold using molding sand, a caking additive is mixed into the molding sand, the mixture is loaded into a mold metal frame and the molding sand is hardened to thereby mold a mold.
Here, the mold metal frame is normally formed in a cuboid body, and a size thereof is determined according to the maximum width, height and length of a product. In this mold metal frame, since a wide clearance is produced due to a shape of a product that is not similar in shape to the mold metal frame, a large quantity of molding sand must be loaded into this clearance.
In order to cope with this, there have been proposed a sand reducing method using a jig such as a jig of a type for mounting a partition having a shape similar to a product onto the inner surface of the metal frame and a jig of a type in which a pipe type or block type jig is loaded together with sand. However, these jigs are low in the general-purpose property and thus are not suitable for multi-product production.
In view of this, as disclosed in PTL 1, there is proposed a method in which two semispherical iron-made cups are spot welded together into an iron-ball-shaped hollow ball having a clearance and the hollow ball is loaded among molding sand.
In this method, specifically, when loading molding sand into a molding frame, in a clearance formed between the molding frame and a product due to the shape of the product, there is disposed a hollow ball constituted of two semispherical cups which have been put together by spot welding with a given clearance between them. This may reduce the quantities of molding sand and caking additive used with a high general-purpose property. Also, since the clearance is secured using a spot welding method as the cups connecting method, the pressure of the internal expansion air of the cup produced due to the heat of the molten metal may be relieved.